Process of recovering the soda content of waste liquor.



H. K. MO0RE. PROCESS OF RECOVERING THE SODA CONTENT OF WASTE LIQUOR.APPLICATION FILED MAR. 6, 1913. 3 1,1873%, Patented May 4,1915.

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APPLICATION FILED MAR. 6, l9l3 1,137,779. Patented May4,1915.

2 SHEETSSHEET 2.

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HUGH K. MOORE, OF BERLIN, NEW HAMPSHIRE.

.t'ROCESS OF RECOVERING THE SODA CONTENT OF WASTE LIQUOR.

Specification of Letters Patent.

Patented May 4, 1915.

Application filed March 6, 1913. Serial No. 752,865.

Liquors, of which the following is a specification.

This invention has relation to the production of cellulose fiber fromWood, and, while it has relation more particularly to the manufacture ofsulfate pulp so-called, yet certain features may be employed in makingeither soda or sulfite fiber.

In the manufacture of pulp, great quantities of coal must be used inmaking steam for use in the digesters and for other purposes connectedwith the process, and there is a constant waste of materials, all ofwhich increase the cost of production.

The purposes of the present invention, briefly stated, are to reduce theconsumption of coal, to reclaim valuable materials heretofore wasted,and to make a better product than heretofore possible.

I shall explain my invention as used in the manufacture of sulfate pulp.

On the drawing, Figure 1 illustrates conventionally and more or lessdiagrammatically the inst-rumentalities which may be utilized inpractising my process. Fig. 2 illustrates a collector for the pulp whichhas heretofore been wasted. Fig. 3 represents one of the evaporators forthe black liquor so-called. Fig. 4 represents the fuel drier and thefeeding and mixing devices which supply the black liquor and the carriertherefor. I I

Heretofore' it has been the customary practice to evaporate the ligninor black liquor (from the digesters by the use of disk evaporators andto deliver the concentrated residuum to a rotary incinerator throughboth of which are passed the products of combustion from a smeltingfurnace. The concentrated residuum is delivered from the the incineratorin a partially charred mass known asv blackash from which the water andmost of the volatile combustibles have been expelled. This black ashcontains most of the soda which went intothe digesters for cooking thewood chips, and for the recovery of the soda it is mixed with salt cake,so-called (sulfate of soda, Na,SO,,) and burned in a smelting furnace,the smelted soda being delivered to a dissolving tank containing water.Ordinarily when the solution reaches the-required strength(approximately 20 B.), lime is added to causticize the carbonate ofsoda, after which the supernatant liquor, containing sodium sulfid (NaS), sodium sulfate (Na SO sodium hydrosulfid (NaHS) and sodium hydrate(NaOH), is with drawn, leaving the carbonate of lime in the tank, and isused for the next cooking.

According to my invention, I utilize the lignin or black liquor inmaking steam which may be employed in the digestion of the raw wood,thus reducing the consumption of coal, and I dispense with the use ofthe disk evaporators and rotary incinerators as I find that theutilization of direct heat is expensive and wasteful.

Briefly speaking, I employ multiple-effect evaporators in concentratingthe black liquor, and with the residuum I mix sulfate of soda and acarrier of any carbonaceous material. The mixture is then dried and isfed into the smelting furnaces. The products of combustion, after theyhave performed their Work in making steam, are

carried through the drier for the drying of the mixture. The melted sodaor other inorganic content from the smelting furnace is then treated inthe usual way. It might appear at first glance that the results might beaccomplished merely by using a multipie-effect evaporator for theconcentration of the black liquor, but this is practically impossiblebecause of the character of the residuum. When black lignin liquor isevaporated down to dryness, it is found to be of such character that itis practically impossible to handle it by any known means. liquid butwhich is soft enough so thatnone lump put on top of another will mergeinto a solid mass. It cannot be chopped, broken It is a tar-like masswhich is not a or handled in any known way. I find that, I byevaporating and condensing the black liquor to approximately 35 B., thatis'to about the consistency of treacle, it may be mixed with sawdust,pulverized bark,

hogged wood or'peat, coke free from iron,

or other carbonaceous material, and that when so mixed it may be handledby a conv wise be discharged with the steam into the a carried into thenext tank'to wash it.

charged into the as will be e.

veyer and otherwise manipulated and then burned. l v

On the/accompanying drawings, 10 indicates a digester to which thechipped wood is fed from a receptacle 11. The liquor is tank-35 into theNo.

the usual false bottoms, theconduit for the contents of the digesterbeing indicated at 15 and being valvedat l6 and 17 The pulp isdischarged iron the tanks 13 and .14 through spouts into a conveyer 18.When the pulp and lignin'liquor was discharged into one or the other ofthe tanks 13, 14 at atmospheric pressure, a large volume, of steamarises which is discharged through a conduit 19 intoa collector 20,shown in detail in Fig. 2. The function of the collector 20 is tocollect the pulp which would other-.

air. In detail, it consists of a metallic casing 20 the lower endofwhich is an in verted cone. The inlet port from. the conduit 19 isarranged tangentially so that the steam and pulp which it carries areswirled around'inside of the tank.

At 37,38 I have indicated muti le-efiect evaporators for the blackliquor. nly two combined condensers and evaporators are shown, but inpractice I prefer to use a quintuple effect. The black liquor is forcedby a pump 39 through a pipe 40 from the 1 evaporator 38. The partiallycondensed liquor is carried by the pipe 41 into the N o. 2 evaporatorindicated at 37, and so on through the series. After the black liquorhas been evaporated to approximately the consistency of treacle or 20indicates an eduction conduit which.

extends'down into the conical lower end of the casing, and which nearthe upper end of the casing is provided with apertures 20.

The pulp, which remains in the collector, is discharged through thevalve, outlet 20 into a tank 21. The steam, when'freed from the v I ofcondensation, the latter being respectively 100 provided with a trap 50and a pump 51.

condenser 25, so that its heat may be utilized in heating water tob'eused in washing the.

tanks 13 and 14. Water,

entering the con- 1 denser through a pipe 26, after being heated isconveyed through a pipe'27 to a hot water tank 28. From this tank theheated water 1s forced by a pump 29 through a pipe 30,

branch pipes 31, 32, connected by valved, branches to the severalcompartments of the tanks 13 and 14. The tanks 13 and14 are connectedin'the usual way by a pipe 33 so that the water used to wash one tankmaybge e black liquor and the water used to wash the tanks may bedischarged from the tanks 14 into tanks or receptacles 34, 85 which areconnected by a pipe 36 as shown. It is from these tanks that the.blackliquor is dismultiIple-eifect eva orator lained. 't will'be un erstoodthat, while have shown but one digester and but two wash tanks 13- and14, there may be a series of digesters and also a semess of washtanksaccording to the requirements of the'milL.

. mixing chamber is substantially 35 36., it is forced through the pipe42 into a mixer as will be explained.

As a matter of detail, it will be noted that steam isintroduced into thefirst condenser 38 through a valved pipe 43. In Fig. 3, one

of the combined condensers and evaporators is shown. It has thepartitions 38, 38 with a large corrugated central conduit 38. The blackliquor passes upwardly through the tubes 38 and down through the centralconduit 38, the partially concentrated black liquor passing out throughthe pipe 41 at the bottom of the evaporator. From the top of theevaporator a steam pipe 44 passes into the condensing chamberof the nextevapora- V tor. From the last eva orator, which in this condensers andevaporators are provided with a pipe 48 for the relief of the containedair and. also with pipes 49, 49 for the water 52 indicates the pipe forsupplying the condenser 46 with-a cooling medium.

It will be understood that the parts are not shown in Fig. 1 at theirrespective levels since the figure is a diagrammatic illustration ofthe: parts. Their relative dimensions are roughly indicated and suchinstrumentalities as pumps are indicated in the most conventionalmanner. 1

After the lignin or black liquor has been condensed to approximately 35B., it is forced through the pump 53 through the I pipe 42, which isvalved as at 54, 'to atrapped funnel 55 leading to a mixingchamber 56 asbest shown in Fig. 4. This substantially cylindrical and is providedwith a helicoid or worm conveyer 57 which may be driven from anysuitable source of diumof a belt pulley or sprocket 58. With thereceiving end of the casing communicates a hopper 59 into which isdischarged, from a traveling conveyer 60, sawdust, peat or othercarbonaceous material, together 125 w1th a certain amount. of sulfate ofsoda. The black liquor is discharged into power through the memam-.70

receivi 1g endso that the carbonaceous material and the black liquor arethoroughly mixed and intermingled as they are passed through the casingby the worm conveyer.

which the material may fall to the partitions 63. Extending upwardlythrough the drier there is a shaft driven by any suitable form ofgearing from an external source of power. Secured to this shaft areradially extending arms 66 provided with scrapers 67 These scrapers arearranged at such an angle that the material on the partition 63 isforced outwardly, whereas the material on the partition 64 is forcedinwardly, thus insuring the feeding of the material downwardly frompartition to partition until it is finally discharged from the lowerpartition 63 into the bottom of the casing, where there is an inclinedoutlet chute 68. The dried material is forced out through the outlet byscrapers 69 on radial arins 70 affixed to the shaft 65. The driedmaterial, which is discharged through the chute 68, falls intoareceptacle 71 from which it is lifted by a bucket conveyer 72 anddelivered to a belt conveyer 7 3 from which it is discharged into thecombustion chamber 74 ofthe combined smelting furnace and boilerindicated as a whole at 75. Ihave not shown the combined smeltingfurnace and boiler in detail, but it will be understood that thecombustion chamber is provided with twyers as at 93 through which airblasts are delivercd to the chamber to insure the proper combustion.From the bottom of the combustion chamberthere is a well 7 6 to receivethe melted soda or other inorganic content and from which the lattercontinuously flows in. molten condition to a mixing tank 7 7 containingwater. The products of combustion from the combustion chamber 74 arecarried through the boiler which is indicated as a whole at 78 and isdelivered through a con.- duit 79 to a fan 80 by which they are forcedeither into the atmosphere through a stack 81 or else through a conduit82 to the top of the drier 62. The hot products of combustion passdownwardly through the drier into contact with the material to" be driedand pass outwardly through an eduction stack 83 to the atmosphere.

At 84 I haveshown a gate damper for deflecting the products ofcombustion either through the stack 81 or through the conduit 82. Fromthe boiler 78 the generated steam is carried to the steam main 85, avalved branch 86 of which supplies the digesters, and the aforesaidvalved pipe 43 supplies the multiple-eflect evaporators.

In operation, the digesters are filled with chipped wood, after I whichthe alkaline liquor usually containing sodium sulfid, sodium sulfate,caustic soda and sodium hydrosulfid is delivered into the digester so asto fill it. The cover is then placed upon the digester and steam isinjected so that the contents will be cooked at approximately 100 poundspressure. After the cooking has been completed, the contents ofthe'digester are blown into one or the other of the tanks 13 and 14.Inasmuch as the interior of the tank is at approximately atmosphericpres-- sure, great volumes of steam are evolved which are emittedthrough the conduit 19 and are blown into the casing 2-0. Here the pulp,which is carried off with the steam, is collected, the freed steam beingeither admitted to the atmosphere or else carried through the condenser25. to heat the Water which issubsequently used for washing'the tank.The pulp is removed from the tank 13 or 14 as the case may be and theblack liquor containing the lignin content is discharged into one or theother of the tanks 34. The tank is then washed so as to remove all ofthe black liquor which may remain therein. It will be understood that,where there is a series of tanks, they will be subjected to a series ofwashings, the water being discharged into one or the other of the. tanks34, 35. The waste or black liquor is then pumped to the multiple-effectevaporators or condensers from which it is discharged in a conditioncontaining between 50% and 60% solid matter or at 35 B. It is thensubstantially of the consistency of treacle and is forced by the pump tothe mixer 56 where it is mixed with sawdust, pulverized bark, hoggedwood, coke or the like, and also with the necessary quantity of sodiumsulfate. Where there are in a mill one or more of the old types ofrotary incinerators, the black ash may be used as the carrier for theconcentrated black liquor. After the black liquor and its carrier aremixed, they are delivered to the drier. The hot gases from the smeltingfurnace are forced under pressure through the drier at a temperatureranging-from 400 to 550 F., the temperature of the gases leaving thefuel drier ranging from 220 to230 F. The hot gases travel through thedrier in the same direction with the material to be dried so that thereis little liability of the material being ignited by sparks carried withthe hot gases. 'As the mixture of hot; liquor and ts of soda is reducedby the carbonaceous mat ter to sodium sulfid. Undoubtedly part of thissulfate is reduced as follows:'

.Na,SO,,+4G=Na,Sf-4CO; with the subsequent formation of carbonate asfollows:

Na O+CO,=Na,CO

The smelted soda flows continuously from the well 76 into the water inthe tank 77. The carbonate of soda passes into the solualso and

I tion without change, the sodium sulfid breaking up as follows:

Na ,S+H,O=NaHS+NaOH.

When the solution in the tank 77 reaches the desired strength,(approximately 20 B.), it is pumped to the alkaline room where therequired amount of lime is added to causticize the carbonate of soda aspreviously explained.

The mixture, containing the black liquor, sodium sulfate and thecarbdnaceous material,

is of relatively high specific gravity so that it will not be carriedaway by the tremendous air blast which is necessary in order to burn it.The flue gases from the furnace generate the steam necessary foroperating the plant and act to dry the mixture as explained.

I have ascertained that the evaporated black liquor from the digestercontains very nearly 6,000 British thermal units per pound of solidmatter, and, by the method which I have described, I am able to utilizethe heat in the generation qf steam for operating the mill. r

The process which I have described has numerous advantages. Even whereit is necessary to operate a single coal-burning furnace in the mill totake care of the g0 and come, it is possible to save approximately 75%of the fuel heretofore necessary. Again, owing to the thorough mixtureof the sulfate of soda with the black liquor, the effluent from thesmelting furnace contains a better mixture for making sulfate pulp thanhas been possible heretofore. For example, there is amuch greaterpercentage of sulfid of soda in the aqueous solution in the tank 77 thanhas been heretofore possible. Another advantage which I have found isthat, by passing the flue gases from sage of the gases caused by theshelves or partitions, and the problem was tointroduce solid matter intothe drier and remove it therefrom, and at the same time prevent theemission of the flue gases. This problem was solved by feeding the solidmatter and black liquor to the mixer 57 in which was the helicalconveyer, and also by delivering the dried material through the chute 68into the receptacle 71,,thus preventing the emission of the gases atthese points.

To insure against the possibility of the passage of. the gas through themixing chamber, I connect the delivery end of the mixing chamber withthe drier by a conduit 90 inwhich is interposed an exhaust fan 91.

A damper is employed, as indicated in dotted lines at 92, so that Isecure practically a balanced draft. In consequence of thisconstruction, any gases that get into the mixing chamber are immediatelyreturned to the fuel drier with possibly a little air that may be suckedfrom the hopper and mixing chamber.

As a matter of detail in the construction of the drier, I line it withcement consisting of plastic material such as a mixture of tar andasbestos or any other suitable cement, so that the flue gases will notcome in contact with the metallic casing The greatest efliciency issecured by properly insulating with heat-insulating material the variousconduits and pipes and the drier, the pulp collector, etc., into whichheated liquids or gases are delivered or bywhich they are conducted fromone point to. another.

While I have described more or less in detail the instrumentalitieswhich I utilize in carrying out my invention, since they are the bestforms nbw known to me, it will be understood that my invention is notlimited in its entirety thereto and that various changes may be madewithout departing from the spirit and scope of the invention. So far asI know, I am the first to mix the concentrated black liquor with acarbonaceous carrier and to burn the mixture to recover theinorganiccontent of said liquor; alst to dry the mixture by the flue gasesresulting from the combustion of another portion of the mixture, andalso to utilize the same flue gases in making steam for employment inthe digesters and for such other purposes as it may be necessary to useit. The fact that the concentracted black liquor is mixed with thecarbonaceous carrier enables it to be handled and dried. The blackliquor is absorbed on the surfaces and in the pores of the carrier tosuch an extent that it does not form a sticky mass which cannot bemanipulated. When properly mixed and dried as herein described, thesawdust or other carrier will be delivered from the drier saturated withthe solid matter from the black liquor and will be of high specificgravity.

Having thus explained the nature. of my said invention and described away of making and using the same, although without attempting to setforth all of the forms in which it may be made or all of the modes ofits use, what I claim is:

1. The herein described process of treating the waste liquor resultlnfrom the digestion of wood which conslsts in mixing the liquor with acarbonaceous carrier, burning the mixture, and simultaneously smeltingand recovering the inorganic content of the said liquor.

2. The herein described process which consists in mixing the ligninliquor with a solid corbonaceous carrier, supplying air under pressureto and burning the mixture in a. smelting furnace, smelting thecontained soda, and recovering the soda.

3. The herein described process which consists in mixing lignin liquorcontaining soda with a carbonaceous carrier and sodium sulfate,supplying air under pressure to and burning said mixture, smelting thesoda, and recovering the smelted soda.

4. The herein described process of recover-. ing soda from the wasteliquor resulting from the digestion of wood which consists in mixing theliquor with a carbonaceous carrier and sodium sulfate, burning a driedmixture of said liquor and said carrier, smelting the contained soda andrecovering the same, and drying the first-mentioned mixture by contactwith the gaseous products of combustion resulting from burning a likedried mixture.

5. The herein described process which consists in mixing lignin liquorwith a carbonaceous carrier, burning a previously dried mixture of saidlignin liquor and said carrier in a smelting furnace, recovering thesmelted soda, and with the resulting gaseous products of combustiondrying the first-v mentioned mixture.

6. The herein described process which consists in continuouslycommingling and concentrating lignin liquor, continuously mixing a solidcarbonaceous carrier with the concentrated liquor, continuously feedingthe mixture to a combustion chamber, continuously burning said mixtureand smelting the inorganic content of the concentrated iiquor, andcontinuously recovering said inorganic content in molten condition.

7. The herein described process which consists in continuouslyconcentrating lignin liquor, continuously mixing a carbonaceous materialwith the concentrated liquor, continuously drying said mixture,continuously feeding said dried mixture to a smelting furnace,continuously burning said dried mixture and smelting the inorganiccontent of said liquor, and continuously withdrawing said inorganiccontent in molten condition.

8..,The herein described continuous process which consists in burning ina smelting furnace a dried mixture of carbonaceous material, ligninliquor and sodium sulfate, smelting and recovering the contained soda,mixing another body of lignin liquor and carbonaceous material, anddrying the lastmentioned mixture by passing the products of combustionof the first. mentioned mixture in contact therewith.

9. The herein described continuous process which consists incontinuously concentrating lignin liquor, continuously burning in asmelting furnace a dried mixture of carbonaceous material, concentratedlignin liquor and sodium sulphate to recover the soda in the ligninliquor, passing the products of combustion through a boiler for theproduction of steam, usin said steam in the concentration of ligninliquor, mixing another body of concentrated liquor and carbonaceousmaterial, and drying the lastmentioned mixture by passing said productsof combustion in contact therewith.

10. The herein described process which consists in continuouslyevaporating and condensing the waste liquor from a digester toapproximately 35 B., continuously mixing a carbonaceous carriertherewith, continuously drying the mixture to a combustible condition,continuously burning said mixture and smelting the inorganic contentthereof, and recovering the smelted content.

11. The herein described process which consists in continuously burninga dried mixture of lignin liquor residuum and a carbonaceous carrier ina smelting furnace, continuously mixing aqueous lignin liquor and saidcarrier, continuously passing the gaseous products of combustion intocontact with said mixture to dry it, continuously feeding said driedmixture into said furnace to be thus burned, and continuously smeltingand recovering the inorganic content of said mixture.

12. The herein described process which consists in continuously burninga dried mixture of lignin liquor residuum and a carbonaceous carrier ina furnace, continuously mixing aqueous lignin liquor and said carg I1,137,77e

rier, continuously feeding said mixture to In testimony whereof Ihave'aflixed my the furnace to be thus burned, and cofntinusignature, inpresence of two Witnesses. ously passing the gaseous products 0 com--bustion into contact with and in the direc- HUGH MO 5 tion of movementof said mixture thus being Witnesses:

fed, foridrying said mixture previous to its WALTER P. ABELL, beingburned. JOHN E. PovEY

